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Artifacts associated with implementation of the Grangeat formula
Seung Wook Lee1, Gyuseong Cho, Ge Wang
1CT/Micro-CT Laboratory, Department of Radiology, University of Iowa, Iowa City, Iowa 52242, USA. swleee@ct.radiology.uiowa.edu
Medical Physics
|January 7, 2003
Summary
Exact cone-beam reconstruction in medical x-ray CT can produce artifacts like thorn, wrinkle, and V-shapes. Strategies to mitigate these include data extrapolation, smooth interpolation, increased sampling, and noise suppression for clearer images.
Area of Science:
- Medical Imaging
- Computed Tomography
- Image Reconstruction
Background:
- Approximate cone-beam reconstruction in medical x-ray CT often introduces image artifacts.
- Exact cone-beam reconstruction algorithms aim to eliminate these artifacts but face challenges in numerical implementation.
- The Grangeat algorithm is a key exact reconstruction method.
Purpose of the Study:
- To investigate and characterize image artifacts associated with the Grangeat algorithm.
- To identify the causes of specific artifacts: thorn, wrinkle, and V-shaped.
- To propose methods for artifact mitigation in cone-beam CT.
Main Methods:
- Analysis of the Grangeat algorithm applied to a circular scanning locus.
- Examination of artifact formation in the radon domain and detector planes.
- Evaluation of data extrapolation, interpolation techniques, sampling rates, and noise suppression.
Main Results:
- Identified thorn artifacts due to inappropriate radon domain extrapolation.
- Identified wrinkle artifacts from non-smooth derivative interpolation between detector planes.
- Identified V-shaped artifacts on the meridian plane from abrupt data transitions.
Conclusions:
- Thorn artifacts can be removed by filling the shadow zone with continuous data.
- Wrinkle artifacts are suppressed by avoiding nearest-neighbor interpolation and using bilinear interpolation with sufficient projections.
- V-shaped artifacts can be reduced by increasing sampling rates and suppressing data noise.